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A variable frequency drive operating at 48 hz or 1400 (approx) RPM will
be operating on 50% of kW or HP. At 30 hz and below it is operating at
cube root of HP. Energy savings are obvious, however, you need to know
the 'fan curve' to know if you have 'fallen off' the curve at 2000 cfm.
What does this represent in terms of RPM. If the fan is producing 9000
cfm at 60 hz, if linear, the motor will be turning at 300 rpm at 15 hz.
We would not recommend rpm less than 10 hz as there will NOT be
sufficient air moving across the motor windings to dissipate the heat
generated in the motor.
2) The drive does not care, less than 30 hz as explained above.
3) We like A C TECH, manufactured in the United States.
Further......If you 'turn down' the amount of air across your coils, you
will be dropping your discharge temp considerably. Keep in mind that as
with any centrifugal pump or fan, at such slow RPM you are doing very
little work. You will be doing little more than 'stiring the pot'.
Best of luck.
John A. Hook
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